Marantz 1550 output breakdown

P

pyrus

New Member
My good old Marantz 1550 receiver doesn't like loudspeakers anymore... When you power it on, everything works okay as long as I connect a headphone. But as soon as I connect a loudspeaker (8 ohms), output power nearly breaks down and it gives only a very flimsy, weak sound.

Can anybody please help me with a) advice or, even better b) a service manual/schematic? I suspect some defect in the power regulation since one high-power resistor is getting VERY hot, and the regulation power transistor seems to be too hot for my taste, too. But I'd like also to check the voltages in the amp section - maybee the hot power supply is only a followup of the generic problem.

many tks, Robert
 
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Hi Robert,
I have the same exact problem, and wonder how did you fix it. Hope you are still checking your inbox to get my message :)
Best regards
Aziz
 
Aziz Abboud said:
Hi Robert,
I have the same exact problem, and wonder how did you fix it. Hope you are still checking your inbox to get my message :)
Click to expand...
This is a very old post. Robert is long gone. So, get the manual from HiFi Engine. Then come back and tell more about the offending components.
 
PE9ZZ said:
This is a very old post. Robert is long gone. So, get the manual from HiFi Engine. Then come back and tell more about the offending components.
Click to expand...
Hi :)
Thank you for the promot reply :)
Upon receiving the amp, I cleaned all pots excluding the main selector, switched it on and headphones were working however the speaker output was very distorted and not normal. Balance right was better sounding than left. Both channels were very weak despite the distortion.
After cleaning the selector, one speaker channel worked fine and tge other far low and distorted.
Phono was not working.

I recapped the whole power board section and the main filter caps. Noticed that 2sd613 was preciously replaced by an sd 313 which is not good. I re-repkace it with an sd243c.

Phono now works on headphone, so as everyhing normal on headphone but output on speakers is distorted on both channels again :( with one loud and distorted and other low and distorted.

I have not replaced 2sd415 (Q708) and 2sd549 (Q707) yet.

NB. Resistor 801 replaced by 220 ohms instead of 200 though in either case gets extremely hot in less than 40 seconds.

Sorry for the long reply.
Regards
Aziz






I have download the service manual, checked idling current and offset voltages and they are almost correct.
 
Clean/replace speaker system switches. There is nothing else between the amp output and the headphone connector.
 
PE9ZZ said:
Clean/replace speaker system switches. There is nothing else between the amp output and the headphone connector.
Click to expand...
Tried speaker system 2 and same result as system1.
Cleaned switch of system 1 speakers no change in distortion nor difference between left and right speaker ( both distorted yet one far louder than the other).
 
Absolutely sure headphone sound is very clear. No scope unfortunately. I am trying to unsolder one of the system switches to disassemble and thoroughly clean it.
If the headphone section is working doesnt that mean preamp is ok? Is the headphone amplification done by the preamp or the power amp? Do i assume my output transistors are ok?
 
Aziz Abboud said:
Absolutely sure headphone sound is very clear. No scope unfortunately. I am trying to unsolder one of the system switches to disassemble and thoroughly clean it.
If the headphone section is working doesnt that mean preamp is ok? Is the headphone amplification done by the preamp or the power amp? Do i assume my output transistors are ok?
Click to expand...
Follow up:
Unsoldered system2 switch, opened it up and thoroughly cleaned it. After that therewas no change in sound(still same problem)
 
Aziz Abboud said:
Is the headphone amplification done by the preamp or the power amp?
Click to expand...
Look above. The headphones get exactly the same signal as your speakers. Maybe they went phut? Try different speakers? Or different amp? Apart from the speaker switch there is NOTHING between the amp and the speakers. Except wires and speaker terminals.
 
Steven Tate said:
See if you are getting 35V DC at J812. If yes, then see if idle current and DC offset can be set to spec on each side. Instructions are on page 5 in service manual available on hifiengine.com. Also, here is a pertinent thread.
https://audiokarma.org/forums/index.php?threads/marantz-1550-smoke-smell.630895/
Click to expand...
Steven Tate said:
See if you are getting 35V DC at J812. If yes, then see if idle current and DC offset can be set to spec on each side. Instructions are on page 5 in service manual available on hifiengine.com. Also, here is a pertinent thread.
https://audiokarma.org/forums/index.php?threads/marantz-1550-smoke-smell.630895/
Click to expand...
Hi Steven,
Thank you for the hint.
I am getting 35.6- 35.7 dc. Idle current adjusted to 23.9 on both channels. As to offset do i keep my speakers plugged in the terminals and test the dc offset ( ofcourse without signal), or remove the speakers and test the output?
Nb. I dont have an 8 ohm resistor for testing

Thanks and regards
 
PE9ZZ said:
Look above. The headphones get exactly the same signal as your speakers. Maybe they went phut? Try different speakers? Or different amp? Apart from the speaker switch there is NOTHING between the amp and the speakers. Except wires and speaker terminals.
Click to expand...
Will do that in a bit. I have exchanged Q708 and Q710 as they looked messy, applied thermal pasted and reclipped one channel and testing; now the relay does not start ( though parts exchanged are exact numbers). Will check for any solder issue.
 
Looks like you're getting ahead of yourself. First test the things that are relevant. Like your speakers. Swapping transistors is not going to help you. As demonstrated. You have introduced another fault. Do you have a multimeter?
 
Yes I have a multimeter. The transistors I exchanged as they looked messy and I happen to have them :)
Am changing the other set to check if relay will click, to be able to test the other speakers
 
If relay was clicking before you changed the parts and not after, you know what that means. I agree about finding and fixing the problem before changing random parts. When it comes time to check DC offset, input on Aux, volume to zero, speakers connected are OK. But need to find out why relay won’t click first.
 
Aziz Abboud said:
Am changing the other set to check if relay will click
Click to expand...
Changing is not fault finding. You must realize that a relay click is not a goal in itself. I never wait for that but hook up a multimeter directly to the amp's output instead. If at switchon the voltage settles to zero I know it is OK and will come out of protect. If it doesn't I switch off and start faultfinding.
 
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